This invention relates to a magento-resistive linear position sensor. More specifically, this invention relates to a linear position sensor which uses magneto-resistive elements to sense the direction of the magnetic field as a sinusoid signal which is indicative of object position.
It is desirable in many applications to determine the precise position of various objects which linearly traverse a defined path. For example in the case of an exhaust gas reciprocating (EGR) valve which is used to control the amount of exhaust gas which is recirculated into a cylinder, it is highly desirable to accurately determine the position of the valve in order to precisely control the amount of gas which is allowed back into the cylinder. An accurate measurement of the valve position allows the optimal amount of gas to be recirculated thus increasing engine performance but avoiding an overabundance of exhaust gas which may prevent the cylinder from firing.
Linear position sensing is presently performed using a variety of electrically based sensor devices. Present linear position sensors include linear voltage differential transducers (LDVT), variable inductance, variable capacitance and eddy current killed oscillators. LDVT and variable inductance sensors determine linear position by means of a rod inserted in a coil or coils of wire. The rod""s position is determined by measuring the amount of inductance or current through the coil or coils. As the rod is inserted into the coil or coils, the inductance measured changes. The position of the rod is thus roughly proportional to the amount of measured inductance or current. Calculations may be made to convert the measured inductance or current to a linear position representation. However, these solutions create problems with regard to cost, measurement resolution, accuracy and packaging. While these systems can be made to function, they tend to be expensive and often lead to packaging issues in their application. For example, in the case of an LVDT, two coils are required thus doubling the size of the sensor package and increasing the cost of the sensor.
In contrast, eddy current and capacitance based position sensors measure frequency. The frequency of the signal depends on the position of the target. A common method for sensing linear position involves using a magnet connected to a displaceable member such as a rod or piston and measuring the magnetic field from the magnet. The magnetic field measurement is roughly proportional to the distance from the magnet. Thus, the position may be determined through a series of calculations for the measured magnetic field.
Such present methods suffer from several problems. Most significantly, the magnetic field strength, inductance strength and current strength are not exactly linear which introduces error in the position measurement. This inaccuracy increases as the magnetic field, or inductance or current reach further distances away from the transducers for measurement of the fields.
Additional solutions have included using a linear magneto-resistive transducer in conjunction with a moving magnet. The magnetic field sensed by the transducers is an indication of the position of the magnet. However, the non-linear nature of the magnetic field results in distortions near the ends of the traversal of the magnet. Such distortions may be corrected, but such corrections require extra circuitry or processing which increase the complexity and cost of the device.
Thus, there exists a need for a linear magnetic position sensor. There is also a further need for a position sensor which uses magneto-resistive elements with simple circuitry. There is also a need for a linear position sensor which provides a more accurate linear positioning signal than present positioning sensors.
The present invention is embodied in a linear position sensor for determining the position of a moveable object having two magnets generating a magnetic field. The two magnets are spaced apart in a perpendicular plane to the plane of traverse of the object. The sensor has a first magnetic field transducer which detects the generated magnetic field and outputs a first sinusoidal signal representative of the magnetic field direction. A second magnetic field transducer detects the generated magnetic field and outputs a second sinusoidal signal representative of the magnetic field direction. A signal processor unit is coupled to the first and second magnetic field transducers. The signal processor unit outputs a signal which is a function of the sinusoidal signals representative of the position of the object relative to the first and second transducers. The magnets are placed in an angular relation to each other in order to optimize the linear relation between the sinusoidal signals and the actual position of the object.
The invention is also embodied in a method of determining the position of an object. Two magnets are fixed on an object. The two magnets are set at a predetermined angle to provide an optimal linear response based on the sinusoidal variation of the magnetic field produced by the magnets. The magnetic field direction produced by the magnets is detected. The detected magnetic field direction is converted into sinusoidal signals. The position is then determined based on the sinusoidal signals.
It is to be understood that both the foregoing general description and the following detailed description are not limiting but are intended to provide further explanation of the invention claimed. The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the method and system of the invention. Together with the description, the drawings serve to explain the principles of the invention.